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Thread: how do I slit pipe in half
02-22-2005, 09:08 AM #1
I have 4" diameter pipe with a 1/16" wall which is 10 feet long. I need to slit the pipe in half lengthwise. The cut needs to be clean and straight . I thought about my local laser shop, they could cut one side then index it and cut the other side but their laser head will not raise high enough to clear the top of the pipe. A bandsaw blade would be too wavy and give a sloppy cut.
Sooo.. I am looking for any suggestions to slit this pipe lengthwise into two equal c shaped sections. I will need to cut up to 50 pieces of pipe.
02-22-2005, 10:15 AM #2
Perhaps set the pipe into a piece of angle and use the angle for a guide for a plasma cutter?
02-22-2005, 10:23 AM #3
Do you have a vertical band saw? If so, put the widest blade you can on there. Then build a guide out of a larger piece of pipe, one that the 4" just slides through. Clamp that larger pipe on the table centered on the blade and let er rip. As long as you get the pipe started straight it will run straight.
02-22-2005, 02:15 PM #4
For tubing with a 16 gage wall I'd say the plasma cutter is the way to go, and a handheld one used in conjunction with a guide strip would do a good job and probably take less time than would be required to set up and index the material on a CNC plasma burner. Cold finished flat bar makes a good guide strip because the slick finish lets the operator drag the torch smoothly. Most handheld cutters use nozzles with a slight step on the face that serves as a contact surface for the guide strip. I've used 1/8x1 flat in the past as the guide and it works fine with our handheld cutter which is a 40A Hypertherm using the standard Hypertherm nozzles. If I were doing 50 of these, I'd roll about 4 C-shaped semi circles from the same 1/8 flatbar to conform to the tube OD, and tack them to 2 guide strips such that the guide edge has the proper offset from the tube centerline to put the actual cut on center. Then it would be a simple matter of clamping the fixture onto a piece of tube and going at it. Clamping up the fixture and making both cuts should take well under ten minutes total.
02-22-2005, 03:08 PM #5
You didn't mention what material your pipe is made of, but I tried to do a similar operation long ago not knowing better and I had a surprise. I milled a long slot in a piece of thin-wall tube to act as a guide slot, kind of like a keyway but the whole way through the tube wall. The tube must have had a ton of stress in it because once cut it sprang open to a substantially larger diameter.
I would be interested to know if there are any types of tubing or stress-relieving processes for standard tubing that will allow the original shape to be maintained after cutting completely through the circumference.
02-22-2005, 03:21 PM #6
Excellent point Chris. If the tube is hot formed then it will be relatively stress-free. If its cold formed from strip, then its going to have plenty of stresses to make it want to spring apart. Past that, the question of whether it was cold formed from either hot or cold rolled strip would make a further difference, with cold rolled strip causing more residual stress. I believe most light gage tubing is cold formed from cold rolled strip, as the hot rolled strip doesn't get along too well with their seam welding equipment. That would yield a product with the max amount of residual stress, but if the material is over-rolled in the forming process such that it isn't necessary to force it together to close the joint for welding, then it may hold its shape very well after splitting. Probably one of those try it and see situations.
02-22-2005, 03:53 PM #7
The material is 4" diameter steel exhaust tubing originally made for semi trucks. It is probably cold formed. I'll cut a small section of it apart to see how much spring back it will have. I have a Miller plasma cutter taht I could set up to do the job, but I was looking for an easier answer.The only other answer would to be able to find a "D" shaped piece of tubing with 2" diameter bend on a 1/16" wall. The only D shape tubing I can find is heavy structural steel for architectural uses with thick wall thickness.
Any other ideas will be greatly appreciated.
02-22-2005, 04:15 PM #8
Yep, its definitely cold formed from CR strip. Walker Manufacturing used to have a plant here where they ran millions of feet of exhaust tubing. Their QC department would reject a tractor trailer load of slit to width coil stock in a heartbeat for the presence of the slighest amount of rust anywhere. If there's a spot of rust on an edge, the welding process ends up leaving a hole at the point of the rust. Unless you've ever seen it done, its hard to imagine just how fast they can make that stuff.
If you need the half sections in full 10 ft lengths then splitting the tubing would be about the simplest way to go IMO. In shorter lengths, rolling would be an option, but a set of 4'-16ga rolls has a 3" roll diameter, and anything longer than 4' is going to have even bigger rolls, so about 4' would be the max length that you could expect to have rolled to shape easily.
02-22-2005, 04:26 PM #9
02-22-2005, 04:59 PM #10
What length do you need?
Could this be rolled on a rolling brake(wrong terminology-its for sheet metal, although yours is a bit on the thick side) of sufficient width?
Could you heat up some steel and press it between 2 pieces of pipe of the correct size (kind of like hot forming between 2 dies?)
02-22-2005, 05:41 PM #11
I think you came close with your first posting - but instead of laser, find someone with a bed-type plasma cutter that will lift high enough.
For your interest, a sheetmetal guy we use has a plasma cutter which does 3D, he can lay a long (ie roadside lamp post) on his machine and it will cut out a large rectangular opening (later covered) for access to the inside of the post, wiring etc. This is done on a tapered pole too if I remember correctly. The head follows the radius of the pipe.
02-22-2005, 06:27 PM #12
There are quite a few water jet machines out there with 10' table travel. The way to go.
02-22-2005, 06:34 PM #13
What's the finished product look like?
02-22-2005, 08:12 PM #14
The finished part (1/2 of the pipe) will be welded up next to the long side of a piece of 2x4 tubing (11 Gauge wall) It will be 8 feet long and will be part of an air table (too detailed to describe here).
02-23-2005, 06:37 AM #15
One way to get the curved pieces you want is to make a simple die out of a piece of pipe split for the female die and a piece of round bar for the male die and form the metal in a brake press. Fifty pieces may not be cost effective but it is another way to get the job done.
02-23-2005, 01:00 PM #16
Sounds like a typical resaw operation so should be doable on a bandsaw. Wide blade with a fine tooth pitch. The trick is a fence with a gentle curvature at the blade with a finger/feather board to hold the tube against the fence. Place a fixture at the backend of the tube to prevent rotation and to ride against an extended fence to prevent cocking.
02-23-2005, 04:23 PM #17
"There are quite a few water jet machines out there with 10' table travel. The way to go.
This probably would not work so well. Water jets do not like to have to cut through interupted shapes. The jet becomes highly distorted after cutting the upper layer resulting in an unperdictable cut on the bottom side.